At present, future worldwide phosphorus resources exhaustion is predicted, and from the domestic conditions that securement of phosphorus resources is dependent on importation, attention is paid to the technique for recovering phosphorus contained in the wastewater.
Heretofore, as for phosphorus in the wastewater, discharge of phosphorus into the environment system is a factor of eutrophication, hence removal of phosphorus and discharge state management thereof have been regarded as indispensable, and thus efforts have been concentrated mostly on the phosphorus removing technique. As representative phosphorus removing techniques, there are the biological phosphorus removing method utilizing phosphorus-accumulation capability of microorganism, and phosphorus removing method based on the coagulating sedimentation.
In order to use these phosphorus removing methods as direct phosphorus recovery/utilization means, for example, processes of incineration, chemical treatment, and the like of excess sludge resulting from the biological phosphorus removing method have been required, and it has been necessary to use a large amount of chemical agents, and arrange a plurality of treatment processes. For example, in order to reuse the phosphorus as resources, it is also necessary to eliminate influences of the used chemical agents and impurities contained in the derived sludge, and hence adjustment and refinement processes of the phosphorus also become necessary. In view of these circumstances, attention is paid to a water treatment technique utilizing a phosphorus adsorbent configured to selectively adsorb phosphorus. Examples of a material used to selectively remove an anion include a phosphorus adsorbent in which an anion-exchange resin or hydrotalcite-like inorganic layered compound is basically used as an anion exchanger, and adsorbent in which various metals are basically used as an anion exchanger. Regarding methods of manufacturing these adsorbents, a phosphorus adsorbent formed by developing the material characteristics of the above adsorbents, and phosphorus recovery utilizing the phosphorus adsorbent, a large number of methods are proposed.
As an example of a phosphorus recovery system utilizing the above-mentioned adsorbents, there is a system disclosed in JP-A 2006-346555(KOKAI).
In JP-A 2006-346555(KOKAI), a wastewater treatment equipment provided with solubilization means, solid-liquid separation means, and phosphorus adsorption means of biologically-treated sludge is described.
In the wastewater treatment equipment of JP-A 2006-346555(KOKAI), the treated matter of the sludge solubilization means discharged by the sludge solubilization means is circulated with biological treatment means, and part of the treated matter is supplied to the phosphorus adsorption means through post-sludge separation means. Accordingly, depending on the form of the sludge separation means, the solid contents are removed and supplied to the phosphorus adsorption means. Although reduction in concentration of the phosphorus in the wastewater is enabled, replacement of the adsorbent, and reuse of desorbed phosphorus are exemplified for the case where phosphorus adsorption is saturated due to lowering of the adsorbent capability, and soluble impurities contained in the water to be treated of the phosphorus adsorbent remain in the phosphorus adsorption means provided with the phosphorus adsorbent. As a result of this, when the adsorbed phosphorus is desorbed from the adsorbent, the impurities of the phosphorus adsorbent contained in the water to be treated are mixed into the phosphorus liquid to be recovered. Accordingly, there is the problem that the exemplified recovery process of phosphate includes impurities.
Further, as another problem, there is the problem that in the phosphorus removal of the wastewater containing phosphorus, when an alkaline liquid configured to desorb phosphorus is passed after the phosphorus is adsorbed/removed with respect to impurities contained in the water to be treated containing phosphorus, the impurities contained in the water to be treated are mixed into the alkaline liquid used to desorb phosphorus in addition to the phosphorus desorbed by the alkaline liquid, and moved to the alkaline liquid which has been passed, and hence the impurities are mixed into the phosphorus recovery liquid.
An object of the embodiments is to provide a water treatment equipment configured to recover phosphorus by making the sludge-separated liquid discharged from a treatment process of sludge discharged from a biological water treatment process the water to be treated, separating the phosphorus contained in the water to be treated from the water by using an adsorbent, and preventing the impurities in the water to be treated from being mixed into the recovered phosphorus.
In general, according to one embodiment, a water treatment equipment comprising a reactor vessel including an absorbent packed bed filled with a phosphorus adsorbent configured to adsorb phosphorus contained in the water to be treated, an introduction path configured to introduce the water to be treated into the reactor vessel, a discharge path configured to discharge the water to be treated from which phosphorus has already been removed from the reactor vessel, water passing means for passing a phosphorus desorption agent liquid configured to desorb phosphorus from the phosphorus adsorbent which has already adsorbed phosphorus through the reactor vessel, phosphorus recovery means for acquiring phosphate from the phosphorus desorption agent liquid which has been subjected to the passing treatment, and an upward flow formation path connected to a lower part of the reactor vessel, and configured to upwardly introduce a liquid into the reactor vessel to form an upward flow after the water to be treated which has been held in the reactor vessel is discharged from the reactor vessel.